Method and device for energy-saving leak testing of a fuel tank system, in particular of a motor vehicle

ABSTRACT

In order, in a diagnostic unit ( 70 ) for leak testing of a tank system ( 10 ) of an internal combustion engine, to allow minimization of the energy consumption during a diagnostics test and simultaneously prevent the emission of fuel gases, a sleep/wake-up mechanism ( 270, 300, 350 ) is described, in which the diagnostic unit ( 70 ) enters a sleep mode for a selected time interval after the internal combustion engine is turned off, the diagnostic unit ( 70 ) enters a wake-up mode at the end of the first time interval and at least acquires the measurement data necessary for the diagnostics test in the wake-up mode; the diagnostic unit ( 70 ) then enters the sleep mode again during the diagnostics period, and the diagnostic unit ( 70 ) is switched off at the end of the diagnostics period.

BACKGROUND INFORMATION

[0001] The present invention relates to a method and a device foroperating a diagnostic unit for leak testing of a tank system of aninternal combustion engine, in particular of a motor vehicle,measurement data necessary for the leak testing being acquired during adiagnostics period after the internal combustion engine is turned off.Furthermore, the present invention relates to a diagnostic unit suitablefor carrying out the method.

[0002] A method and a diagnostic device for leak testing of a tanksystem of a motor vehicle is known from U.S. Pat. No. 5,263,462, forexample. During a shutoff phase of the motor vehicle, the tank system issealed off using a solenoid valve and, during a longer diagnostics time,the pressure and temperature characteristics in the tank are detectedusing a sensor system and transmitted to the control unit.

[0003] If a partial vacuum builds up during the diagnostics time whilethe tank cools off, the air tightness of the tank system is inferredtherefrom.

[0004] This procedure has the disadvantage that the control unit must beswitched on during the entire diagnostics time. In addition, thesolenoid valve must also have power supplied to it continuously duringthe diagnostics time. This requires a high energy consumption during theshutoff phase, which significantly loads the electrical system of thevehicle. These problems may be counteracted by a higher performancedesign of the vehicle electrical system, which, however, causes highercosts. The diagnostics period may also be reduced, which in turn reducesthe reliability of the diagnosis.

[0005] In a mechanism, previously disclosed by Siemens andDaimlerChrysler in SAE Toptec 99, Indianapolis, the tank is sealed offfrom the environment by passive non-return valves, which close withoutcurrent and, therefore, do not consume any energy in the sealed state.However, if the tank is heated, overpressure builds up in the tankduring the shutoff phase which, if there is a leak, results in fuel gasand/or vapor, which contains hydrocarbons, being able to escape from thetank system into the environment. In addition, a detection electronicsystem must also have current supplied to it continuously during theentire diagnostics time in this case.

[0006] Furthermore, in German Patent Application No. ______ (referencenumber R. 38041 of the applicant), which is still unpublished and towhich reference is made in its entirety in the present context (inparticular to FIG. 3 therein and the description), a device forlow-emission operation of a fuel tank system is described which has,among other things, an activated carbon filter for dissipating excessfuel gases, a controller, and, in particular, a currentless bistablesolenoid valve, which remains in the closed state and in the open statewithout current. A current pulse is only necessary for switching betweenthese two states. The controller is electrically connected to a firstpressure sensor positioned inside a fuel tank and a second pressuresensor positioned outside the fuel tank. Corresponding temperaturesensors are also indicated as alternatives. From the pressure dataacquired, the controller evaluates whether a partial vacuum oroverpressure is to be expected in the tank after the vehicle is turnedoff. In the case when the analysis of the pressure data indicates that,after the vehicle is turned off, an overpressure in relation to theambient pressure is to be expected, the solenoid valve is opened inorder to conduct the excess fuel gas into the environment via theactivated carbon filter and therefore with low emission. In contrast, incase of an expected partial vacuum, the solenoid valve remains closed,after which the leakage test using the partial vacuum may be performedin accordance with the procedure suggested in U.S. Pat. No. 5,263,462.

[0007] Using this device, the emission problem described above islargely eliminated. In contrast to U.S. Pat. No. 5,263,462, the powerconsumption of the solenoid valve is additionally avoided. However, thedisadvantage still remains that the controller must be active for theentire diagnostics time.

SUMMARY OF THE INVENTION

[0008] It is, therefore, the object of the present invention to indicatea method and a diagnostic unit of the species initially described, whichallow minimization of the energy consumption during a diagnostics testas described above and simultaneously also prevent the emission of fuelgases to the greatest extent possible.

[0009] This objective is achieved by the features of the independentclaims. Advantageous refinements constitute the object of the dependentclaims.

[0010] The special feature of the present invention is that, after theinternal combustion engine is turned off, the diagnostic unit enters asleep mode for a selected first time interval; the diagnostic unitenters a wake-up mode at the end of the first time interval and at leastacquires the measurement data in the wake-up mode; the diagnostic unitthen enters the sleep mode again during the diagnostics period; and thediagnostic unit is switched off completely at the end of the diagnosticsperiod.

[0011] The interval operation of the diagnostic unit proposed above,i.e., operation which switches between sleep and wake-up modes,advantageously prevents the diagnostic unit from consuming power duringthe entire diagnostics period, which would significantly stress thebatteries of the vehicle and/or of the tank system during the shutoff orrest phase.

[0012] After the internal combustion engine is turned off, thediagnostic unit may thus either first acquire the measurement datawithin the second time interval and only then go into the sleep mode, orgo into the sleep mode directly after shutoff of the internal combustionengine and only acquire the measurement data for the first time at theend of the first time interval.

[0013] Via the proposed wake-up mechanism, the diagnostic unit may bereactivated at regular time intervals for a second time interval, i.e.,in particular the measurement time period. Following wake-up, thediagnostic unit then reads in the sensor signals necessary fordiagnosis, i.e., the internal tank pressure and, if necessary, theexternal tank pressure, as well as the internal tank temperature and, ifnecessary, the external tank temperature.

[0014] The diagnostic unit subsequently switches off again in order tobe woken up again after a further time interval. The length of the timeintervals, after which the diagnostic unit is woken up, may either bepermanently selected or progressively changeable over time. For example,the time interval may be linearly or non-linearly lengthened, inparticular exponentially, as the shutoff time of the vehicle increasesin order to be adjusted to the leakage behavior of an assumed leak,which also follows an exponential rate equation, and therefore to recordthe measurement data in an appropriately adjusted way. The proceduredescribed may be repeated until there is a diagnostic result or,alternatively, a diagnostics period may be permanently selected.

[0015] It is obvious that the method may be carried out by either thediagnostic unit itself or an additional controller which controls thediagnostic unit. It is also obvious that the sleep mode may represent anactual switched-off mode, for example, in the case of a non-volatilememory for recording the measurement data. In the case of such aswitched-off mode, the diagnostic unit is restarted each time at the endof the first time interval.

[0016] A special variant of the present invention is derived in anapplication in a tank system having a solenoid valve, which opens andcloses without current, and having an activated carbon filter (seepublication German publication ______ cited above), by way of whichexcess fuel gas in the tank system may be conducted to the outside inthe case of overpressure. In this embodiment, in the wake-up mode, thediagnostic unit also determines whether the solenoid valve settingexisting at the moment in question is to be changed and then, ifnecessary, also carries out the change.

DRAWING

[0017] The present invention is elucidated in greater detail in thefollowing with reference to the exemplary embodiments illustrated in thedrawing, from which further features and advantages of the presentinvention are derived.

[0018]FIG. 1 shows a tank system having a diagnostic unit for carryingout the method according to the present invention.

[0019]FIG. 2 shows an exemplary embodiment of the method according tothe present invention on the basis of a flow chart.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0020] Tank system 10 shown in FIG. 1, of an engine (not shown here) ofa motor vehicle, has a tank 20, inside of which a first pressure sensor30 is provided for detecting the internal tank pressure and outside ofwhich a second pressure sensor 40 is provided for detecting the ambientpressure. It is to be noted that, in addition to or instead of bothpressure sensors 30, 40, temperature sensors or the like may also beused in order to acquire the pressure data in tank 20 necessary for atank leak diagnosis.

[0021] Both pressure sensors 30, 40 are connected via signal lines 50,60 to a diagnostic unit 70 according to the present invention. Tank 20has a connection, which conducts pressure, to an activated carbon filter80, which has, among other things, a line 100 connected to a bistablesolenoid valve 90. Solenoid valve 90 also has an exhaust line 110, whichleads to the environment. Solenoid valve 90 may be operated withoutcurrent in the open position and in the closed position. Diagnostic unit70 contains a processor module 120, a permanently powered timer 130, anda comparator (compare-register) 140, which has a negligible currentconsumption.

[0022] Following the shutoff of the engine, and provided that adiagnosis is required, diagnostic unit 70 loads compare-register 140with a time-interval value, after which the next wake-up of diagnosticunit 70 and/or processor module 120 is to occur. When timer 130 has thisvalue, which is entered in compare-register 140, timer 130 triggers theswitching on of processor module 120 via a line 150, which, in thepresent example, is connected to a reset input 160 of processor module120, whereupon diagnostic unit 170 carries out the necessary actions forleak testing, i.e., loading and, if necessary, analyzing the internaltank pressure and the ambient pressure, for example.

[0023] After completion of these actions, compare-register 140 isreloaded with a time interval value, this value representing either apermanently selected value or a value which progressively increases,e.g., exponentially increases, upon each reloading of compare-register140. Timer 130 is likewise reset and restarted. Subsequently, diagnosticunit 70, i.e., in particular processor module 120, if necessary,including pressure sensors 30, 40, is temporarily switched off and/orput into a sleep mode.

[0024] The procedure described is repeated until the diagnostics haveended. At the end of the diagnostics period, timer 130 is no longerstarted before the switch off, so that diagnostic unit 70 then remainspermanently switched off in order to also save energy.

[0025] In the exemplary embodiment, it is also provided that, afterprocessor module 120 is switched on, diagnostic unit 7.0 also checkswhether an overpressure exists in tank 20 according to the pressure dataacquired. If this is the case, it is also checked whether the setting ofsolenoid valve 90 is “open,” so that excess fuel vapor or fuel gas maybe conducted to the outside via exhaust line 110. If the current settingis “closed,” diagnostic unit 70 induces the solenoid valve setting tochange to “open.”

[0026] As an exemplary embodiment of the method according to the presentinvention, FIG. 2 shows a program routine for the use in a diagnosticunit of a motor vehicle described in FIG. 1.

[0027] After start 200 of the routine it is first checked 220, in afirst program loop 210, whether the engine of the motor vehicle isturned off. If this is the case, it is checked 240, in a second programloop 230, whether a leak diagnosis, e.g., in accordance with a higherorder maintenance program (not shown), has been requested. If not, thesequence jumps back to first loop 210. If there is such a request, avalue of a wakeup time, e.g., 5 minutes, is loaded 250 into thecompare-register. Subsequently, the timer is started 260 and thediagnostic unit is set into a sleep mode or switched off 270.

[0028] In a third program loop 280, it is checked 290 whether thecurrent value of the timer is greater than or equal to the wake-up time.If this is the case, the diagnostic unit is set into a wake-up modeand/or switched on 300 and reads out 310 current sensor data forpressure and/or temperature. Subsequently, the compare register isreloaded 320, the timer is reset again 330, and the timer is restarted340. Simultaneously, the diagnostic unit is switched off again 350.

[0029] Using a fourth program loop 360, the steps described above arerepeated until the diagnostics have ended and/or the diagnostics periodis reached 370. After the diagnostics period is exceeded, the diagnosticunit is permanently switched off 380.

[0030] It is obvious that the present invention may be advantageouslyused not only in tank systems of motor vehicles, but, in principle, inall tank systems of internal combustion engines in which leak testing iscarried out during rest operation.

What is claimed is:
 1. A method of operating a diagnostic unit (70) forleak testing of a tank system (10) of an internal combustion engine, inparticular of a motor vehicle, measurement data necessary for the leaktesting being acquired during a diagnostics period after the internalcombustion engine is turned off, wherein, after the internal combustionengine (220) is turned off, the diagnostic unit (70) enters a sleep mode(270) for a preset first time interval; the diagnostic unit (70) entersa wake-up mode (300) after the first time interval elapses and at leastacquires the measurement data (310) in the wake-up mode; the diagnosticunit (70) then enters the sleep mode (350) again during the diagnosticsperiod; and the diagnostic unit (70) is switched off (380) at the end ofthe diagnostics period.
 2. The method as recited in claim 1, wherein thediagnostics period is dynamically determined as a function of theexistence of a diagnostic result.
 3. The method as recited in claim 1 or2, wherein the length of the first time interval is set to progress overtime, in particular, to increase exponentially.
 4. The method as recitedin one of the preceding claims, wherein the diagnostic unit enters thewake-up mode within an at least second time interval and acquires atleast the measurement data within the at least second time interval. 5.The method as recited in one of the preceding claims for a tank system(10) having a switchover valve (90) and a filter (80), by way of whichexcess fuel gas is conducted to the outside via the filter (80) in thecase of overpressure in the tank system (10), wherein the diagnosticunit (70), in the wake-up mode, additionally determines whether thesetting of the switchover valve.(90) is to be changed and then, ifnecessary, induces' the change.
 6. A device for operating a diagnosticunit (70) for leak testing of a tank system (10) of an internalcombustion engine, in particular of a motor vehicle, comprising a sensorsystem (30, 40) for acquiring measurement data necessary for the leaktesting, characterized by means (120) for detecting the shutoff of theinternal combustion engine, timer means (130) for specifying a firsttime interval, and sleep/wake-up means (160), which are used to set thediagnostic unit (70) in a sleep mode and, at the end of the first timeinterval, in a wake-up mode, in which at least the measurement data isacquired.
 7. The device as recited in claim 6 for use in a tank system(10) having a switchover valve (90) and a filter (80), by way of whichexcess fuel gas is conducted to the outside via the filter (80) in thecase of overpressure in the tank system (10), wherein the diagnosticunit (70) has processor means (120), which are used to make adetermination as to whether the valve setting is to be changed, and toinduce a change in the valve setting, if necessary.
 8. A diagnostic unitfor leak testing of a tank system of an internal combustion engine, inparticular of a motor vehicle, characterized by a sleep operation modeand a wake-up operation mode for carrying out the method as recited inone of claims 1 to
 5. 9. The diagnostic unit as recited in claim 8,characterized by timer means (130) for specifying a first time interval,and, upon elapsing of the first time interval, the switch is made fromthe sleep operation mode to the wake-up operation mode.
 10. Thediagnostic unit as recited in claim 9, characterized by at least onecompare-register (140) for recording the first time interval.
 11. Thediagnostic unit as recited in one of claims 8 to 10, for use in a tanksystem (10) having a switchover valve (90) and a filter (80), which areused to conduct excess fuel gas to the outside via the filter (80) inthe case of overpressure in the tank system (10), characterized byprocessor means (120), which are used to make a determination as towhether the valve setting is to be changed, and to induce a change inthe valve setting, if necessary.